In recent years, liquid crystal display devices have come to be widely used in smartphones, personal digital assistants (PDAs), tablet computers, satellite navigation systems, etc. In general, a liquid crystal display device comprises a liquid crystal display panel and a surface illumination device (backlight device) which is overlaid on the rear surface of the liquid crystal display panel and illuminates the liquid crystal display panel. The backlight device comprises a reflective layer, a lightguide plate (lightguide), an optical sheet, a light source such as LEDs, and a rectangular mold frame. The reflective layer, the lightguide plate, and the optical sheet are stacked on each other, and fitted into the mold frame. The peripheries of the reflective layer, the lightguide plate, and the optical sheet are thereby supported and positioned by the mold frame.
As this type of backlight device, the structure in which a mold frame is fitted into a case (backlight cover) made of a metal plate, and further, a reflective layer, a lightguide plate, and an optical sheet are disposed in a cavity of the mold frame has been proposed.
In recent years, as display areas have increased, there has been a continual demand for the frames of liquid crystal display devices to become ever narrower and the liquid crystal display devices to become ever thinner. However, the above-described backlight device including the mold frame is approaching the structural limit of the mold frame, and it is hard to meet the demand for further reduction in thickness and further narrowing of the frame.